U.S. Pat. Nos. 5,073,278 and 5,273,669 teach the stabilization of lubricant compositions with a certain aromatic amine and at least one sterically hindered amine.
U.S. Pat. No. 5,268,113 discloses lubricants stabilized by the addition of a sterically hindered amine and a phenol.
It is known and customary to add stabilizers to lubricants based on mineral or synthetic oils in order to improve their performance characteristics. Antioxidants are of particular importance. Oxidative degradation of lubricants plays a significant role especially in motor oils because of the high temperatures prevailing in the combustion chambers of the engines and the presence, in addition to oxygen, of oxides of nitrogen which act as oxidation catalysts.
Hindered amine compounds are effective stabilizers for lubricants. However, they are generally not employed due to detrimental effects such as seal swell.
The present invention described the stabilization of lubricant compositions with a certain class of hindered amine compounds. The present lubricant compositions are non-aggressive towards seals.